The present invention relates to a magnetic storage device and, particularly, to a magnetic storage device having a lead frame member.
A magnetoresistive effect is a phenomenon that electric resistance is changed by applying a magnetic field to a magnetic material and used in magnetic sensors and magnetic heads. Particularly, Fe/Cr and Co/Cu artificial lattice films are introduced in Non-patent Documents 1 and 2 as giant magnetoresistive (GMR) effect materials which show a very large magnetoresistive effect.
There is proposed a magnetoresistive effect element which has a non-magnetic metal layer thick enough to lose an exchange coupling function between ferromagnetic layers and a laminate structure comprising a ferromagnetic layer, a non-magnetic layer, a ferromagnetic layer and an antiferromagnetic layer. In this element, one of the ferromagnetic layers and the antiferromagnetic layer are exchange-coupled to each other to fix the magnetic moment of the ferromagnetic layer so that only the magnetization of the other ferromagnetic layer can be easily reversed with an external magnetic field. This is an element commonly known as “spin valve film”. Since exchange-coupling between the two ferromagnetic layers is weak in this element, magnetization can be reversed with a small magnetic field. Therefore, a spin valve film can provide a high-sensitivity magnetoresistive element as compared with the above exchange-coupled film. FeMn, IrMn or PtMn may be used as the material of the antiferromagnetic layer. This spin valve film is used in a reproducing head for high-density magnetic recording, and a current is applied in the in-plane direction of the film at the time of use.
Meanwhile, Non-patent Document 3 discloses that a magnetoresistive effect is obtained even by using a perpendicular magnetoresistive effect in which a current is applied in a direction perpendicular to the surface of a film.
Further, Non-patent Document 4 discloses a tunneling magnetoresistive (TMR) effect obtained by a ferromagnetic tunnel junction. This tunnel magnetoresistance makes use of the fact that the size of a tunnel current in a direction perpendicular to the surface of a film is changed by making the magnetization directions of the two ferromagnetic layers parallel or antiparallel to each other with an external magnetic field in a three-layer film consisting of a ferromagnetic layer, an insulating layer and a ferromagnetic layer.
Research into the use of GMR and TMR elements in nonvolatile magnetic random access memories (MRAM) has recently been reported in Non-patent Documents 5 and 6, for example.
To use the above elements in MRAM, GMR and TMR elements are arranged in a matrix, a current is applied to a wiring provided separately to apply a magnetic field, and two magnetic layers forming these elements are controlled to be parallel or antiparallel to each other, thereby recording “1” and “0”. Reading is carried out by using a GMR or TMR effect.
Currently, MRAM comprising TMR elements is mainly under study. This is because MRAM comprising TMR elements can obtain a larger output voltage due to an MR change rate (MR rate) of 20% or more at room temperature and a large resistance at a tunnel junction. Further, MRAM comprising TMR elements does not need to carry out the reversal of magnetization at the time of reading, thereby making it possible to read with a small current. Therefore, MRAM comprising TMR elements is expected to be used as a low power consumption type MRAM capable of high-speed writing and reading.
In the write operation of MRAM, the magnetic characteristics of the ferromagnetic layers in the TMR element are desirably controlled. Stated more specifically, a technique for controlling the relative magnetization directions of two ferromagnetic layers sandwiching a non-magnetic layer to be parallel or antiparallel to each other and a technique for reversing the magnetization direction of one magnetic layer in a desired cell surely and efficiently are desired. A technique for controlling the relative magnetization directions of two ferromagnetic layers sandwiching a non-magnetic layer to be parallel or antiparallel to each other within the plane of a film by using two crossing wirings is disclosed in Patent Documents 1, 3 and 4, for example.
Patent Document 3 teaches that the memory cell of MRAM requires two crossing wiring layers, magnetic storage elements, transistor elements, and a coupling member for electrically coupling the magnetic storage elements and the transistor elements. Each of the magnetic storage elements has a recording layer which is ferromagnetic, a fixed layer and a non-magnetic layer sandwiched between the recording layer and the fixed layer.
When the cell is made small in size for higher integration in MRAM, a reversed magnetic field is grown by a diamagnetic field, depending on the size of the magnetic layer in the film surface direction. Thereby, a large magnetic field is required for writing, and consumption power also increases. Therefore, a technology for optimizing the shape of the ferromagnetic layer to facilitate the control of the magnetization direction is proposed as shown in Patent Documents 2, 5 and 6.
The control of the magnetization direction is selectively carried out for the recording layer of a specific magnetic storage element with a synthesized magnetic field generated by a current applied to two selected crossing wiring layers.
In recent years, there have been proposed a spin injection system for reversing the magnetization of a recording layer by injecting a spin polarized electron into the recording layer and a domain wall displacement system for controlling the magnetization direction by driving a domain wall formed in the region of the recording layer with a flow of a spin polarized electron (spin polarized current) as systems of controlling the magnetization direction, in addition to the above-described operation system using a wiring current magnetic field.